Multi-axis robotic manipulators, also know as mechanical scanners, are used for performing non-destructive inspections (NDI) of materials in many industries. The designs of such machines vary widely and include X-Y gantry systems, X-Y manipulators, R-THETA manipulators, and Z-THETA manipulators. While the specific designs of such machines vary widely, their theories of operation are similar. Mechanical scanners are used to manipulate a NDI probe in a pre-programmed scan pattern on an inspection surface. An analog signal from the NDI probe is monitored, digitized, and displayed by a data acquisition and analysis system. Position information provided by feedback devices on the scanner is used by the data acquisition and analysis system to develop a two- or three-axis mapping of the NDI information. Typical NDI methods used with this type of machine include ultrasonic testing, eddy current testing, and mechanical impedance testing.
Non-destructive inspections of military and civilian aircraft are currently being performed at various maintenance facilities throughout the United States. Ultrasonic methods and mechanical impedance methods are commonly used to detect disbonds between the outer skin and the honeycomb core in composite aircraft structures such as wings. Such disbonds may be caused by repeated stress reversals or water entrapment within the structures. Eddy current methods are currently being used to detect surface cracking in thin skin aircraft structures such as fuselages. Cracks in the skin commonly develop around fasteners and are caused by repeated stress reversals within the structures.
Most of the NDI of modern aircraft is being performed using manual techniques. These techniques require that a technician manipulate a hand-held probe on the aircraft surface while simultaneously monitoring a NDI instrument. Thus, the quality of manual NDI techniques are highly operator dependent. Moreover, such manual NDI techniques are labor intensive and slow. Still further, NDI data obtained during manual inspections cannot, in general, be saved as a permanent record.
NDI of modern aircraft is currently being performed using a limited amount of automated NDI techniques. Growth in the use of automated NDI methods has been limited due to the complex nature of modern aircraft structures. Typical aircraft surface geometries may be flat, conical, cylindrical, or some combination of the three representative typical surface geometries. The surface curvatures may be convex or concave, while the surface orientations may be horizontal, vertical, or overhead.
Most on-aircraft automated NDI techniques require the use of a mechanical scanner to manipulate a NDI probe, whether ultrasonic, eddy current, or mechanical impedance, in a preprogrammed scan pattern on the aircraft surface. Various aircraft scanner designs exist. These designs include rigid X-Y gantry systems which are supported by floor-mounted bases or which are mounted to the aircraft surface by vacuum cups. Another common design involves the use of a track-mounted, two-axis scanner. In this type of system, a vacuum track is coupled to the surface of the aircraft structure. A two-axis scanner mounts to the vacuum track via guide rollers or magnetic wheels. The X-axis typically coincides with the track axis. A cantilevered Y-axis is oriented 90 degrees relative to the X-axis.
Conventional mechanical scanner designs have seen limited use in aircraft NDI applications because they are not well-suited to the demands of the task. Conventional gantry systems are well-suited for inspecting large areas with flat surfaces but they cannot be adapted conveniently for small diameter curved surfaces or areas with limited access. Conventional vacuum track-mounted scanners can adapt to both flat and curved surfaces, but they can only cover a narrow area due to the cantilevered Y-axis.
Accordingly, a need has been recognized for a mechanical scanner which can be used to perform non-destructive inspections of large area aircraft structures, which can conform to the complex surface curvatures present on modern aircraft, and which is lightweight, less expensive, and has improved speed capabilities and enhanced flexibility in relation to existing designs.